Press brakes are commonly used to shape sheet-like workpieces, such as sheet metal and the like. A conventional press brake has an upper beam and a lower beam, at least one of which is movable toward and away from the other. Typically, the upper beam is movable vertically while the lower beam is fixed in a stationary position. It is common for a male forming punch and a female forming die to be mounted respectively on the upper and lower beams of a press brake.
Typically, the male forming punch has a downwardly-oriented, workpiece-deforming surface (or “tip”). The configuration of this surface is dictated by the shape into which it is desired to bend a workpiece. The forming die typically has a recess that is aligned with the tip of the punch. The configuration of this recess corresponds to the configuration of the workpiece-deforming surface of the punch. Thus, when the beams are brought together, a workpiece between the two is pressed by the punch into the die to give the workpiece a desired bend.
It is often necessary to exchange forming punches and dies when different bending operations are to be performed. Generally, dies mounted on the lower beam of a press brake are readily removed and exchanged for others. However, punches mounted on the upper table of a press brake often are not so easily replaced. For example, in some applications, punches are secured to the upper beam by a clamp. Once the clamp has been loosened, the punch in some cases is removed downwardly, but in other cases must be removed horizontally (i.e., by sliding the punch longitudinally from the clamp). When the clamp is loosened to the point where the punch can be removed downwardly, the punch may accidentally slip and fall. This can cause harm to press brake operators and/or damage to equipment, particularly when using long punches (which can be quite heavy).
A common press brake tool holder design is known as the “American style” and is shown schematically in FIG. 1A with a common American-style press brake punch. As shown in this figure, the bottom portion of the upper beam is so fashioned as to include a plate C, and a heavy bolt BO is employed to attach the plate to the beam TA. The beam and plate have confronting surfaces that bound a downwardly-open recess 8 into which the tang T of the punch TL is received. Typically, the bottom surfaces B of the beam and plate are horizontally aligned and serve as load bearing surfaces for transmitting a downwardly-directed load onto the upwardly-facing shoulders SH of the punch TL.
To mount an American-style punch in a corresponding tool holder, the punch is pushed upwardly into the downwardly-open recess 8 until the load receiving shoulders SH of the punch encounter the load-transmitting surfaces B of the plate C and beam TA. The bolt BO is then tightened to secure the tang T of the punch TL between the plate C and the beam TA. When the punch is to be removed from the holder, the plate C is loosened and the punch, while gripped firmly by the operator, is withdrawn downwardly. To avoid the possibility of accidentally dropping the punch, a safety key historically has been attached to the top of the tang with an edge of the key extending into a groove in the holder. With this arrangement, however, the tool must be removed by sliding it longitudinally from the holder or by disassembling the holder.
U.S. Pat. No. 6,467,327 (Runk et al.), the entire contents of which are incorporated herein by reference, provides-American-style tooling having a particularly advantageous safety mechanism. A tool holder described in this patent (“the '327 patent”) has walls defining a downwardly-open, tool-receiving recess. The walls of the tool holder define both a downwardly-facing, force-delivering shoulder adjacent the bottom of the tool-receiving recess and a shelf within the recess having an upwardly-facing surface that is spaced upwardly from the downwardly-facing, force-delivering shoulder. The tool comprises a body having a lower workpiece-engaging surface, an upwardly-facing, force-receiving shoulder engageable with the shoulder of the tool holder, and an upwardly-extending tang receivable in the tool holder's downwardly open recess. The tool includes an actuator that is spaced below the tool's force-receiving shoulder. A safety key is coupled to the actuator for movement horizontally into and out of alignment with the tool holder's shelf. Thus, the '327 patent provides a highly advantageous American-style tool that can be removed downwardly from the tool holder and yet offers the ability to loosen the clamp (or “plate”) on the tool holder without risking immediate dropping of the tool.
FIG. 1C depicts another style of tooling that is commonly referred to as Wila-style tooling. Characteristically, a Wila-style tool holder has a horizontally-extending safety slot S/S, and a Wila-style tool has a movable projection P that, in use, extends outwardly through an opening in the side surface of the tang tool into the safety slot. Reference is made to U.S. Pat. No. 5,245,854, the entire teachings of which are incorporated herein by reference, for additional details on Wila-style tools and tool holders.
As described in the aforementioned patents, a safety key can be moved into engagement with a tool holder by a spring that biases the safety key toward an extended position, and the safety key can be disengaged from the tool holder (and moved to a retracted position) by operating an actuator on the tool. For example, a button on the tool can be depressed to move the safety key toward the retracted position (against the bias of the spring). Thus, the spring alone keeps the safety key in its extended position. This is less than ideal in some respects. For example, when a tool is being positioned or repositioned on a tool holder (e.g., when sliding the tool along the tool holder), it may be difficult to assure the spring will keep the safety key engaged with the tool holder at all times. This may be particularly difficult to assure when the spring force weakens substantially over time. Press brake operators are thus required to carefully position and reposition such tools on a tool holder in case the safety key is inadvertently retracted during such movement of the tool in the tool holder. Inadvertent retraction of the safety key may otherwise cause the tool to fall unexpectedly from the tool holder. Thus, it would be desirable to provide a tool having a safety key that is movable between extended and retracted positions and that can be locked in its extended position.